Instructions
Log in to Facebook and launch the "Farm Town" application from the left side of your profile. Repeat this process in up to five new tabs or windows. The number of tabs or windows will dictate the number of layers you create.
Click the "Connection" button that looks like a plug and appears in the upper-right corner of the screen. Select the green tick to work with the farm offline. The plug icon should turn red. Repeat this process in the other tabs or windows.
Press the "Plow" button on the bottom-right of the game screen to plow each field. You need to plow the area you want to stack in the same way in each field.
Plant the seed with the longest harvest time in the first tab or window. Sow all of your seeds in the first farm before moving to the next one. Click "Save" when your avatar has finished planting them. Close the tab or window.
Repeat Step 4 until one tab or window remains open. Instead of closing the tab or window, click "Save" and then "Play" to refresh your farm and stack your crop layers into one farm.